This invention relates to a stent delivery catheter system, such as the kind used in percutaneous transluminal coronary angioplasty (PTCA) procedures. More particularly, it relates to a stent delivery catheter employing two retractable sheaths which may be retracted to release a self-expanding stent, a balloon assisted expandable stent or a balloon expandable stent.
In typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient and advanced through the aorta until the distal end is in the ostium of the desired coronary artery. Using fluoroscopy, a guide wire is then advanced through the guiding catheter and across the site to be treated in the coronary artery. An over the wire (OTW) balloon catheter is advanced over the guide wire to the treatment site. The balloon is then expanded to reopen the artery. The OTW catheter may have a guide wire lumen which is as long as the catheter or it may be a rapid exchange catheter wherein the guide wire lumen is substantially shorter than the catheter. Alternatively, a fixed wire balloon catheter could be used. This device features a guide wire which is affixed to the catheter and cannot be removed.
To help prevent arterial closure, repair dissection, or prevent restenosis, a physician can implant an intravascular prosthesis, or a stent, for maintaining vascular patency inside the artery at the lesion. The stent may either be a self-expanding stent, a balloon assisted expandable stent or a balloon expandable stent. For the latter type, the stent is often delivered on a balloon and the balloon is used to the expand the stent. The self-expanding stents may be made of shape memory materials such as nitinol or constructed of regular metals but of a design which exhibits self expansion characteristics.
In certain known stent delivery catheters, a stent and an optional balloon are positioned at the distal end of the catheter, around a core lumen. The stent and balloon are held down and covered by a sheath or sleeve. When the distal portion is in its desired location of the targeted vessel the sheath or sleeve is retracted to expose the stent. After the sheath is removed, the stent is free to self-expand or be expanded with a balloon.
In a coronary stent deployment system which utilizes a retractable sheath one problem which is encountered is the interaction of the sheath and the stent upon retraction of the sheath. Typically, as the sheath slides off of the stent, the stent is subjected to potential marring by the sheath. While this problem can be minimized by making the sheath of soft materials, such materials are often unsuitable for use with a self-expanding stent where prolonged storage results in creep deformation of the inner sheath.
It is desirable to provide a medical device delivery system which provides a protective, non-marring inner sheath for the medical device and is capable of retaining the medical device for brief periods of time and which further has an additional outer sheath over the inner sheath which is capable of retaining the medical device for lengthy periods of time, thereby allowing the device to have a suitable shelf life.
The present invention provides a medical device delivery system in which two sheaths, an inner sheath and an outer sheath, cover a medical device mounted on the distal end of the medical device delivery system. In its various embodiments, the invention contemplates a delivery system in which the inner sheath is either a tear away sheath or a retractable sheath and the outer sheath is either a retractable sheath or a pull away sheath.
In accordance with the present invention, the outer sheath is desirably constructed to be more creep resistant than the inner sheath. The outer sheath may be made of a material having a higher hoop strength than the inner material. The inner material should be capable of retaining the medical device in place on the delivery system for at least a short period of time before it either is retracted or opens due to material failure. The outer sheath should be capable of retaining the medical device for longer periods of time so that the device may have a reasonable shelf life.
To this end, the invention provides a medical device delivery system comprising a manifold at the proximal end of the delivery system. Extending distally from the manifold is an inner tube. At the distal end of the inner tube is a medical device mounting region for concentrically mounting a medical device thereon. Covering the medical device mounting region, at least in part, is a distal inner sheath attached to the inner tube at the distal region of the inner tube. The distal inner sheath is concentrically disposed about the inner tube. The medical device delivery system also comprises a distal outer sheath, concentrically disposed about the inner tube. At least a portion of the distal outer sheath is disposed about at least a portion of inner sheath.
In one embodiment of the invention, the distal inner sheath is a tear away sheath and the distal outer sheath is retractable by means of an outer sheath retraction device. The outer sheath retraction device extends in a distal direction from the manifold. The distal outer sheath extends from the distal end of the retraction device.
In another embodiment of the invention, the distal inner sheath is retractable by means of an inner sheath retraction device. The inner sheath retraction device extends in a distal direction from the manifold. The distal inner sheath extends from the distal end of the inner sheath retraction device. Similarly, the outer sheath is retractable by means of an outer sheath retraction device. The outer sheath retraction device extends in a distal direction from the manifold. The distal outer sheath extends from the distal end of the outer sheath retraction device.
In another embodiment of the invention, the distal inner sheath is retractable by means of an inner sheath retraction device. The inner sheath retraction device extends in a distal direction from the manifold. The distal inner sheath extends from the distal end of the inner sheath retraction device. The distal outer sheath contacts the inner sheath, and extends proximally from the distal region of the inner tube. The distal outer sheath is removed prior to insertion of the device in the body.
In all of the embodiments, the delivery system may further comprise the medical device mounted on the medical device mounting region. Among the contemplated medical device for use with this system are stents and grafts. Desirably, the stent will be self-expanding or a balloon assisted expandable stent.